Pam Jenoff has created a story that you won't want to put down. I love the cover--that alone would have been difficult for me to resist. The characters are, for the most part, well developed, and Emma's/Anna's involvement with the Jewish resistance makes for a driving plot.
At times, I confess, I found the internal dialogue feels tedious--she keeps having the same argument with herself. But this conflict is actually part of what makes it readable. How often do you have an argument with yourself about a major decision just once?
One problem I did have was Anna's insistence that she "had no choice" throughout the last half of the book, when her aunt-in-law Krysia made it very clear in the beginning that there's always a choice. I don't know if it's that I think she needs to be called out for the choices she's made, or if I just didn't like her refusal to acknowledge that these were her decisions, for which there would be consequences.
The only character who was underdeveloped was the Kommandant himself, but I'm not sure that we would find his so irresistible otherwise.
An intense and enjoyable book. If I rated on a five star scale, I'd give it four stars.